A chain saw is basically made up of three components. The power head includes a motor that drives a sprocket. A guide bar is attached to and extends outwardly from the sprocket of the power head. A cutting chain is entrained on the guide bar to be driven by the sprocket and guided by the guide bar for cutting operation.
The guide bar is typically an oval-shaped metal plate defining along its edge an oval path for the cutting chain. The plate or bar is typically about 0.150 inch thick and the path around the bar edge is characterized by a center groove of about 0.050 inch width flanked by side rails also of about 0.050 inch width. The saw chain is made up of side links and center links. Tang portions extend from the center links into the groove and ride in the groove to assure entrainment of the saw chain around the guide bar periphery.
Early versions of the guide bar were produced from a single thickness metal plate, e.g. a 0.150 inch thick plate with the center groove around the bar edge being machine cut. The metal plate material and the process of cutting the groove are high-cost items and have been the target for many years in development efforts to reduce the overall cost of a chain saw. A secondary factor, concerns the excessive weight of the chain saw, with the solid steel bar contributing substantially to that weight.
Out of these development efforts came the laminated bar. Using the above example, it will be appreciated that two 0.050 inch thick outer side laminates and a 0.050 inch center or core laminate, properly configured and assembled, will produce the oval-shaped bar with edge groove. The total materials cost is somewhat reduced but, more importantly, the expensive groove cutting operation is eliminated. However, added to the production cost is the cost of fastening the laminates together, typically accomplished by spot welding.
It has long been recognized that the center or core laminate does not require the high strength characteristics of steel. Numerous proposals have been made to replace the core with a lighter, less expensive material. Examples of such developments are described in U.S. Pat. Nos. 3,473,581 (Merz), 3,191,646 (Merz), 4,693,007 (Apfel), and 4,383,590 (Pantzar).
The problem with these prior proposals is that replacement materials somewhat reduce weight and materials cost but add new problems that have generally resulted in as high or higher total production cost. Fastening the outer laminates in the appropriate relative spacing is a major consideration. Also, not previously discussed, is the desirability of forming the grooves so that the oil for lubrication can be injected into the groove and available for the various sliding components, i.e. the saw chain's side links sliding on the bar rails and the tang of the center link sliding along the sides of the bar groove.